Conventionally, stepping motors of the PM (permanent magnet) type, for example, have been widely employed as actuator components in a variety of kinds of industrial fields, most of which stepping motors are comprised of a rotor having a permanent magnet in the hollow space of two sets of annular stator cores with exciting coils exhibiting the magnetic action for rotation-drive of the rotor; recently, the stepping motors are becoming more important for use also as drive sources for analog measurement instruments due to the fact that such motors are less in dimension and yet significant in drive torque.
One typical stepping motor of this type has been disclosed in, for example, Published Unexamined Japanese Patent Application (PUJPA) No. 5-64411 and PUJPA No. 8-111971, wherein the stepping motors disclosed are designed to include two annular bobbins with exciting coils each wound for a corresponding annular stator core while securing a plurality of current-carrying terminals to these annular bobbins to thereby provide electrical connections with respective exciting coils and a circuit board via the current-carrying terminals.
Incidentally, the former of those disclosed in said Japanese documents is designed so that the current-carrying terminals are distributed for fixation to the annular bobbin of each annular stator core, whereas the latter of them is such that the current-carrying terminals are concentrically secured together to the annular bobbin of certain one of respective annular stator cores, which is one-side (upper-side) annular stator core.
However, the former of those motors disclosed in said Japanese documents with the current-carrying terminals residing dispersedly is disadvantageous in that when winding and mounting the exciting coil around the one-side (lower-side) annular bobbin, certain part of the current-carrying terminals must obstruct the outer periphery of a winding section so that the current-carrying terminals badly behave as a bar to the exciting coil windings, which should require that an extra winding-work area be provided or reserved by causing such current-carrying terminal part serving as a bar to be spaced far from the annular bobbin, which would result in an increase in size. On the other hand, the latter of the stepping motors disclosed in the Japanese documents with the current-carrying terminals being disposed concentrically is such that since no current-carrying terminals are provided at the annular bobbin of the other side (lower side) of annular stator core of respective annular stator cores , no parts are present for supporting the termination end of such exciting coil, which in turn makes it difficult to independently execute winding at the annular bobbin of the other-side (lower-side) annular stator core to thereby necessitate execution of winding after combination of respective stator cores (annular bobbins), thus resulting in a decrease in assembly efficiency while having to allow the current-carrying terminal provided to the annular bobbin of the one-side (upper-side) annular stator core to badly act as a bar to winding on the annular bobbin of the otherside (lower-side) annular stator core, which leads to the necessity of letting such part of the current-carrying terminal acting as a bar to winding be significantly separated from the annular bobbin thereby increasing the size as in the case of the former motor disclosed in the Japanese document stated supra.
The present invention has been made in view of the above points, and one primary object is to provide a stepping motor capable of increasing the assembly work efficiency and yet avoiding an increase in size by facilitating mounding at separate winding steps an exciting coil with respect to the annular bobbin of each annular stator core while increasing the winding work efficiency by preventing current-carrying terminals from acting as a bar to such winding works.